For sport Novice Penguins (13) at Stathams is good. You can set up a toprope easily and lap it to practice.
For Trad Pink Knickers (12) at Churchmans is probably the easiest low graded climb to set a toprope on and learn leading. The Sting (14) is also good for a slightly different style (Hexes are great there). Come to think of it there are at least half a dozen climbs at Churchmans that will fit the bill and give you a variety of placement options.
If it was a true lead the I would agree with you, but if you are on a toprope pseudo-leading as was suggested in the original post then you will fall out not into the crack, so it won’t be overly dangerous.